1. Field of the Invention
The present invention relates generally to motorized concrete finishing machines. More particularly, the present invention relates to high powered riding trowels that can be varied in width to accept various finishing implements. Representative self propelled riding trowels are classified in United States Patent Class 404, Subclass 112.
2. Description of the Prior Art
As will be recognized by those skilled in the art, freshly placed concrete must be appropriately finished. Motorized trowels have proven to be effective for finishing the surface of wet concrete. There are two major types of motorized trowels, including manually manipulated trowels and larger riding trowels. Each type of trowel employs finishing blades that rest directly upon and frictionally contact the concrete surface to be finished. Hence, the blades support the machine's entire weight.
The trowel is passed over the concrete surface several times as the concrete sets. The pitch of the blades is adjustable. To vary pitch, each trowel blade may be pivoted about its longitudinal axis. Modern practice calls for the use of rotating finishing pans during initial machine finishing to achieve "super-flat" and "super-smooth" floors. A wide variety of manually pushed troweling machines, or power trowels have previously been proposed. However, self propelled riding trowels can finish concrete quicker and more efficiently over larger areas than manual trowels.
Prior art riding trowels generally include some form of frame from which two or more bladed rotors project downwardly. An operator sits atop the frame and controls movement of the trowel through a steering system. The rotors are driven by a self contained motor mounted on the frame, which may be linked to rotor gearboxes. Steering is accomplished by tilting the axis of rotation of the rotors. A yoke controlled bearing assembly is often employed to vary blade pitch. The weight of the trowel and the operator is transmitted frictionally to the concrete by the revolving blades.
Riding trowels typical of those present in the art are disclosed in two patents issued to Holz, U.S. Pat. Nos. 4,046,484 and 3,936,212. '212 is a three rotor riding trowel while '484 is a more popular two rotor trowel. Each of the rotors in the Holz patents has three radially spaced apart blades.
I have been involved with several prior motorized trowel inventions. U.S. Pat. No. 5,108,220 relates to a fast steering system for riding trowels. It discloses a state of the art steering system for riding trowels that enhances maneuverability and control. U.S. Pat. Des. 323,510 also discloses a riding trowel.
Most current, popular riding trowels incorporate two sets of bladed rotors. The sweeps of the rotors overlap to provide a smooth finished surface without an intermediate seam. It is also known in the art to provide a disc-shaped finishing pan device in place of the blades to flatten freshly placed concrete. The advent of more stringent concrete surface finish specifications using "F" numbers to specify flatness (ff) and levelness (fl), dictate the use of pans on a widespread basis. Pan finishing allows surface finishing to proceed sooner after initial placement of the concrete. The larger surface area of the pan lowers bearing pressure. This allows wet concrete to be worked earlier and provides a hydraulic effect upon the concrete monolith. As concrete cures, the interior is in a semi-fluid state compared to the surface. In other words, the surface tends to cure earlier than the interior of the monolith. The pans force the high points downwardly, providing a leveling effect at the surface that improves overall (fl) smoothness. Since the concrete surface can be worked earlier, grout is easily and quickly brought to the surface. The grout can be quickly moved into low points and fill voids, and the pans level the surface to a superior flatness.
The process of working the surface of freshly placed concrete by pan finishing has been established by practiced and experienced builders, skilled in the art. Modern panning of concrete floor surfaces is essential to economically achieve a "super-flat" floor. In practice, the trowel is panned across the slab, then turned to repeat the circuit, advancing about one pan width each pass. This procedure fills voids, works down high points and provides a "super-flat" floor surface finish. Generally, the pans are rotated relatively slowly, at fifty to eighty RPM.
Trowel pans are rotated like bladed rotors. However, the pan normally must have a smaller diameter than rotors, since pans cannot overlap, and must not contact one another. Therefore, the pan covers a reduced area in contrast to the bladed rotor. To overcome this disadvantage and to make full use of trowel engine output, a riding trowel with wider spacing for relatively larger pan drive elements is suggested.
Typically pan finishing is followed by blade finishing. In the final stage of finishing, the trowel blades are adjusted to a relatively high pitch angle and operate at high speed- one hundred-fifty RPM or more. This provides a smooth, slick surface. The prior art suggests the use of two finishing trowels to timely finish a floor before curing.
It is economically disadvantageous with known trowels to first mount pans and then replace them with blades during finishing. With fixed frame trowels, pans that can be retrofitted are too small. Further, horsepower demands upon trowels incorporating large blades or pans are extreme. When large areas are to be troweled, time constraints are important. If for example, a pan-equipped machine is too slow, the concrete in remote slab areas will harden without proper pan finishing. Surface uniformity will suffer, even if subsequently blade-trowelled. Pans affect machine handling. They can make an otherwise versatile machine difficult and cumbersome to handle. Relatively higher horsepower is needed to enable self-propelled, panning trowels to properly steer, even when running relatively slow. However, added horsepower must be properly distributed to the unit, and the steering mechanism must handle the pressure. Hence, it is desirous to provide a power riding trowel that can mount either pans or blades. The machine must be easily convertible at the job site during the finishing of a floor. As a result, a single machine is used to pan finish and blade finish a floor before curing. The cage and drive centers of the trowel must be adjustable outwardly to mount the pans. Critical steering linkages must also adapt.